JPS60112635A - Manufacture of glass optical fiber preform - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to the manufacture of glass optical fiber preforms;
In particular, the present invention relates to a preform manufactured by the process (2) consisting of the collapse of a glass tubular matrix of the preform having a doped quartz core. The term optical fiber preform as used herein means a columnar body with a solid cross section for forming an optical fiber by drawing an optical fiber having an optical waveguide structure therein.

Prior Art and Its Problems One method of manufacturing such tubular preforms involves vapor deposition into the pores of a glass substrate tube. Although the present invention does not only relate to wavelengths of 1.275 to 1.3
Applications include the production of preforms for single mode fibers designed to operate in the 35 micron range. One of the important parameters that determines the performance of the fiber when operating in this wavelength range is the level of hydroxyl contamination in the optical core and the optical cladding of the vapor deposited material directly surrounding the core.

There are three important causes of water N group contamination during the production of preforms by this method. The first typically has about 1
Diffusion from the substrate tube containing 50 ppm + water M groups,
Second, some of the hydrogen-containing contaminants of the feed gas and steam in the gas stream used in the vapor deposition reaction tend to enter the deposition as 1% water; Similar contaminants in the atmosphere within the pores of the tube as it collapses into a preform. The first source of contamination can be at least partially ameliorated by selecting a substrate tube with relatively low moisture content to begin with, or by selecting a deposited optical crete layer of suitable material and thickness to serve as a diffusion barrier layer. Ru. The effects of the second and third causes are improved by using dry ingredients and avoiding leaks in the system that would allow moisture in the air to enter. The second source of contamination, contamination during deposition, is usually because the li product reaction produces hydrogen chloride vapor, which is emitted by the exhaust of the system. The third cause is of lesser importance.

Therefore, in reality, the most important cause of hydroxyl group contamination is collapse. It has been reported that chlorine gas was added to the collapse atmosphere. This is, for example, Electronics Letters (E ElectronicsL cttc
rs) August 28, 1980, Volume 16, No. 18, 6
B, LJ, i-nsuri (B, LJ, published on pages 92-3)
J, Δ1nslie) and others 1. :yo<5 r off chi V
-1' Structure Four Pre-Bearing Long Cow 1 ~ Larollos Single Mode
Fibers J (QptimiSed 5truct
ure forp repair 1. ono L
J 1tra-L OW-1-03S S inglc
-Mo+Ic ``1bres''. Electronics Letters, January 8, 1981, Vol. 17, No. 1, pp. 3-5. J, Arven Ll.
.

Ion (IWa
veleno'th Performance of
0ptical F 111reS Co-Doged
witb F +uorTnc). IEEE Journal of Q u
ant(llll E ICCtrOllioS>Q
'E Vol. 18 No. 4 91 Beta) ≦) Negative J, paper by Ainsley et al.
TheDcsion and Fabrication
of Monomode Optical Fit
+cr), citing their previous paper, chlorine is 1
0% chlorine/acid mixture. Also, the 3rd Ink National Optics and Optical Fiber Comic Cocations (I
international 0ptlicsa Qpt
ical [1bar Communications
)-g-Si Francis 1, 1981, pp. 86-88, ``Reduction of Hydroxyl ]Ttermination in Optical Fiber Preforms J.
(Reduction of l-1ydroxyl
Contamination in Qptical
Fi,ber Preforms) smell'UK,
i, Walker (K, l-, Walker > others,
Explain how the oxidation of silicon tetrachloride and germanium tetrachloride results in 3-10% chlorine in the 11 volume atmosphere, each resulting in an actual level of 40% hydroxyl M contamination.
(decreasing by a factor of about 00). It then explains the use of an atmosphere of 80% oxygen and 20% chlorine for young people (j,).

The present invention involves the use of a much higher proportion of chlorine in a lapse atmosphere than previously reported.

Means for Solving the Problems According to the present invention, the pores of the glass tubular matrix of the preform are made such that the collapsed pores are exposed to a dry atmosphere that does not substantially accommodate hydrogen and hydrogen compounds. The atmosphere consists of chlorine and oxygen, and the content of other components is 10% by volume or less.
A method of manufacturing a solid cross-section glass optical fiber preform having a doped quartz core containing chlorine in the range of 0 to 75 volume percent is provided.

EXAMPLES In the following description, a series of optical fiber preforms were manufactured under substantially the same collapse atmosphere. The attenuation of fiber drawn from these preforms is compared with respect to chlorine R in the collapse atmosphere.

This series of optical fiber preform components are IyJ fabricated by automated equipment using a hydrogen-free thermally induced direct oxidation reaction to deposit glass into the pores of a quartz substrate tube and then collapsed into a preform.

These preforms were fabricated with a vapor phase optical cladding material with a refractive index matching that of the quartz substrate tube, a mode field radius of 5.25 microns, and a 1.5 micron mode field radius.
It is used to produce a single mode fiber with a zero dispersion wavelength of 31 microns and a higher order mode cutoff wavelength of 1.2 microns.

The base tube used is 20ml with a wall thickness of 21+1111
Heralux (@ eralux) with an outer diameter of 11
It is a WG natural crystal tube. The initial deposited material for the optical cladding is quartz doped with germania, phosphorous pentoxide, and fluorine, while the deposited material for the core is quartz doped with germania. The deposition temperature is controlled within ±3°C of the set temperature of 1750°C.

Each coated tube is collapsed at 2050°C into a preform with a nominal diameter of 13 mm by means of a flame feedback control system in both longitudinal sections of an oxyhydrogen burner in which the flame temperature is maintained constant. be done.

Fibers approximately 51v long and approximately 125 microns in diameter are then drawn from the colabus using a vertical bring tower equipped with a ferrite refractory furnace. These fibers are coated on-line with a thermoset silicone elastomer.

The following table shows these preforms! l! This figure shows the collapse atmosphere used in J construction in relation to the attenuation of the fiber drawn from the preform.

Table 1 OH infinite intercept volume at chlorine'a degree 1,385 microns % Absorption peak dB/km, E/km30 1.
63 , 0.03 '30 2.03 0,11 10 3.11 0.04 20 1.79 0.06 34 1.19 0.07 100 0.47 0,25 100 0.35 0.23 38 1 .06 1.0G 80 0.62 0.04 90 0.58 o, 39 9°5 0.39 0.36 80 0.56 0.26 80 0.62 0.09 80 0.63 - 0.31 7/1 0.86 0.15 60 1.15 0.04 Table 2 Preform Chlorine temperature j, 275 - 1.335 microns At 1,385 microns Infinite intercept volume % Average OH absorption in the range of ron No. Maximum attenuation c[
3/km Peak dB/km (B/km5 60
, 0.44 0.72 0.0610 40 0.4
6 1.28 <0.0512, 40 0.51
1.42 <0.0511 29 0.60 4.28
<0.0510 36 0.48 2.54 <0.
059 350.47 2.11 <0.056 35
0.54. 2.11 <0.05 Figure 1 is a graph showing the general shape of the variation of the optical attenuation as a function of wavelength for these single mode fibers. At wavelengths longer than approximately 1.6 microns, the attenuation increases steadily due to the phonon effect, and at the short wavelength end it increases due to the Rayleigh scattering effect. There is a peak 10 of hydroxyl group attenuation at 1 to 2 microns, and an increase 11 of attenuation occurs as the wavelength decreases, but this is due to the cutting-on of higher-order modes.(As the hydroxyl group peak 10 , 1.24-1.
The secondary low peak at 26 microns is clear for water base peak 10 values of 5 dB/kll1 or higher, but is indistinguishable for values of 2 J/km or lower. ) In FIG. 2, the spectral absorption characteristics in FIG. 1 are plotted again against the reciprocal of the fourth power of the wavelength so that the effect of Rayleigh scattering becomes clearer. As can be seen in FIG. 2, the attenuation at a wavelength between the hydroxyl peak 20 and the higher order mode wavelength cutoff 21, for example at a wavelength of 1.31 microns, is the sum of the three components aJ, rbJ and rcJ. Component a is a wavelength-independent portion whose magnitude is given by the tangent of straight line 22 characterizing Rayleigh inverse fourth power low attenuation. Component S is the Rayleigh scattering valve at the selected wavelength and is equal to the product of the slope of the Rayleigh line 22 and the reciprocal of the fourth power of the selected wavelength. The third component C is an additional loss due to the short wavelength end of the hydroxyl peak 20.

For individual fibers, it is difficult to determine the appropriate value of the water MW acid content because it is difficult to determine the exact Rayleigh line 20 of the individual spectral characteristics. However, the relationship between the size of the hydroxyl group peak 20 and the hydroxyl group component C at two specific wavelengths is known from a large number of materials.

This relationship is graphically represented in FIGS. 3 and 4. Therefore, when evaluating the effect of chlorine in the collapse atmosphere, the value quoted for the hydroxyl group component C is
> This is a numerical value derived from the measurement of absorption peak 20. Generally speaking, the results show that as the degree of chlorine increases, the size of the water group C decreases approximately exponentially. This is shown in FIG.

The Rayleigh scattering component depends particularly on the refractive index and varies from material to material. The relationship between the magnitude of this component and the chlorine concentration in the collapse atmosphere is unknown. On the other hand, the wavelength-independent component a, known as the infinite intercept, is as shown in Figure 6 (0,0 in the case of a collapsed atmosphere containing about 50% or less
It remains below 5 J3/km, but increases almost exponentially beyond that.

Based on these results, the effect of changing the m degree of chlorine in the collapse atmosphere can be evaluated by comparing the water I! I base component component infinite intercept a 0.0
5 by adding the value exceeding J3/lv.
As shown in the figure. It can be seen from FIG. 6 that the best chlorine concentration [window] becomes narrower at low chlorine concentrations for long wavelength operation near the hydroxyl absorption peak. Therefore, in the present invention, 30 to 75%
A range of chlorine concentrations of 40
A range of 60% is particularly advantageous.

A separate series of tests was carried out in which oxygen was replaced by helium in the collapse atmosphere, but the size of the infinite intercept still increased almost exponentially as the proportion of chlorine increased. However, in this example the effect was much more pronounced at much lower chlorine concentrations. Therefore, the collapse atmosphere should not contain more than 10% of components other than oxygen and chlorine, and preferably should contain only oxygen and chlorine.

[Brief Description of the Drawings] Figure 1 shows the general form of a typical spectral absorption characteristic of a single mode fiber, with optical attenuation plotted as a function of wavelength; Figures 3 and 4 show the spectral absorption characteristics of the optical attenuation replotted as a function of the reciprocal, and the excess of hydroxyl attenuation at 1.31 microns and 1.325 microns, respectively.
A diagram showing the relationship between the peak value of water M group attenuation at 385 microns, and Figure 5 shows the relationship between the peak value of hydroxyl group attenuation at 1.385 microns and chlorine f in the oxygen-chlorine collapse atmosphere.
! Figure 6 shows the relationship between wavelength-independent (infinite intercept) absorption and chlorine concentration in an oxygen-chlorine collapse atmosphere. Figure 7 shows the relationship between excess attenuation and oxygen water. It is a dimensional diagram showing the relationship between the chlorine concentration in the cable collapse atmosphere. 10.20... Hydroxyl group peak, 11... Increase in attenuation, 21... Higher mode wavelength cutoff, 22... Rayleigh line, a... Infinite intercept, b... Rayleigh scattering component, C...Hydroxyl group component. Patent Applicant Standard Telephones and Cables Public

Claims (1)

[Claims] (1) The T-lapse pores are exposed to a dry atmosphere that does not substantially contain hydrogen and hydrogen compounds. The step of collapsing the pores consists of an atmosphere consisting of chlorine and oxygen, containing less than 10% by volume of chlorine and a range of 30 to 75% by volume of chlorine, having a doped quartz core and a solid state. Cross section of glass optical fiber brief A
-Method of manufacturing (2) The method for manufacturing a glass optical fiber preform according to claim 1, wherein the atmosphere contains salt and fiber in a range of 40 to 6% by volume. G) The method for manufacturing a glass optical fiber preform according to claim 1, characterized in that the atmosphere consists only of salt and oxygen. (4) The atmosphere contains 40 to 60% by volume of chlorine. 6) A method for manufacturing a glass optical fiber preform according to claim 3, characterized in that the tubular preform is formed so that hydrogen and hydrogen compounds are excluded during the deposition of the glass layer in the pores of the glass substrate tube. The method for manufacturing a glass optical fiber preform according to claim 1, characterized in that the preform is formed using a gas phase reaction. (6) The atmosphere contains chlorine at a ratio of 40 to 60% by volume. A method for manufacturing a glass optical fiber preform according to claim 5, characterized in that: ■ An optical fiber preform manufactured by the method according to claim 1. (8) Claim 7 An optical fiber drawn from the optical fiber preform described in Section 3.